The present invention is related to a positioning control of a disk drive capable of performing a positioning control of a head to a target track in a high speed and high precision.
In magnetic disk drive corresponding to one of disk drive, magnetic heads are positioned onto data tracks formed on magnetic disks so as to read/write data from/in the data tracks.
A sector servo system may constitute a major servo system, in which a positioning control of a magnetic head is carried out based upon a servo pattern formed by intermittently recording servo signals on a plane where data are recorded. As a consequence, a controller calculates a control input for controlling the magnetic head in synchronism with an interrupt signal produced by a servo sector so as to execute the positioning control of the magnetic head.
A positioning control system for a magnetic disk drive may be mainly classified into a seek mode and a following mode. In the seek mode, the magnetic head is transported with respect to a target track in a high speed. In the following mode, the magnetic head is followed to a target servo track.
A track which should be followed by a magnetic head is continuously varied due to disk deviations, disk distortions, vibrations of a spindle motor during servo track writing operation, and the like. These factors may be effected as repeatable runout (RRO) in a positioning control system of a magnetic head. Then, these repeatable runout vibrations may cause one of factors which may deteriorate positioning precision of the magnetic head. As a consequence, such a positioning control technique capable of reducing these RRO is necessarily developed.
As one example of such a positioning control technique, JP-A-2001-126421 discloses such a repetitive control system. That is, while a position error signal which has been delayed for one rotation period during following control operation is entered into a filter, a correction instruction which is obtained by multiplying an output signal of the filter by a gain is added to a current position error signal which is not delayed so as to produce a new control output, and then, positional errors are compressed by being followed to RRO.
The technique disclosed in JP-A-2001-126421 may have a better compression effect with respect to low frequency RRO components. However, according to this technique, the compression rate with respect to high-frequency RRO components is lowered due to a low-pass filter installed in a repetitive control unit. In this case, when the cutoff frequency of the low-pass filter is set to be a higher cutoff frequency, there is a risk that the stability of the following control system is deteriorated. Therefore, it is practically difficult to compress the RRO over the entire frequency range.